Technical Field
[0001] The present invention relates to a method and device for controlling an internal
combustion engine.
Background Technology
[0002] Idle stop control for combustion engines is known in the prior art. In idle stop
control, the internal combustion engine is automatically stopped when predetermined
automatic stop conditions are met during idling, and the internal combustion engine
is automatically restarted when a predetermined automatic restart condition is met
during the automatic stop.
[0003] For example, in Patent Document 1, when it is determined that an engine speed is
within a predetermined rotational speed range including a resonance band (resonance
range) of an internal combustion engine during a rotation drop period when the engine
speed drops to zero after the internal combustion engine is automatically stopped,
reverse torque, which is torque on a reverse rotation side, is applied to a crankshaft
of the internal combustion engine by a motor generator to increase the speed at which
the engine speed drops.
[0004] In Patent Document 1, when the engine speed is within the predetermined rotational
speed range, reverse torque is applied to the internal combustion engine by power
driving or regenerative power generation performed by the motor generator, and the
speed at which the engine speed drops is increased, thereby shortening the time required
for the engine speed to pass through the resonance band.
[0005] In Patent Document 1, when reverse torque is applied to the internal combustion engine,
whether to the motor generator is to perform power driving or regenerative power generation
is assessed on the basis of various parameters.
[0006] However, when the engine speed is low, such as when passing through the resonance
band, power generation in the motor generator is hardly possible. Therefore, in Patent
Document 1, there is a risk that it will not be possible to apply sufficient reverse
torque in the predetermined rotational speed range including the resonance band, or
to quickly reduce the engine speed.
[0007] Therefore, in Patent Document 1, there is a risk that when the internal combustion
engine is automatically stopped, it will not be possible to minimize vibration when
the engine speed passes through the resonance band.
Prior Art Documents
Patent Documents
Summary of the Invention
[0009] In an internal combustion engine of the present invention, when there is a request
to restart the internal combustion engine while an engine speed of the internal combustion
engine is decreasing due to an automatic stoppage, the internal combustion engine
is started by resuming fuel injection if the engine speed is equal to or greater than
a predetermined rotational speed threshold at which restarting is possible only by
fuel injection, and the internal combustion engine is started by causing a crankshaft
to rotate using an electric motor if the engine speed of the internal combustion engine
is lower than the rotational speed threshold. When the engine speed of the internal
combustion engine falls below the rotational speed threshold while the engine speed
is decreasing due to an automatic stoppage, an amount of air entering cylinders is
reduced to be less than before the engine speed fell below the rotational speed threshold.
[0010] When the engine speed is equal to or greater than the predetermined rotational speed
threshold, it is possible to ensure the amount of air in the cylinders and prepare
for starting (combustion in) the internal combustion engine by resuming fuel injection.
[0011] When the engine speed is lower than the predetermined rotational speed threshold,
compression reaction force can be reduced and fluctuation in the rotation of the internal
combustion engine can be minimized by reducing the amount of air entering the cylinders
(intake air amount). In the internal combustion engine, it is possible to minimize
vibration when the engine speed passes through a predetermined resonance band of the
internal combustion engine, due to the reduction in the compression reaction force
due to the decrease in the amount of air entering the cylinders.
Brief Description of the Drawings
[0012]
Figure 1 is an explanatory diagram schematically depicting an outline of a system
configuration of an internal combustion engine to which the present invention is applied;
Figure 2 is a timing chart indicating states of control of an internal combustion
engine after automatic stop conditions have been met; and
Figure 3 is a flowchart of a flow of a control for the internal combustion engine
according to the present invention.
Preferred Embodiments of the Invention
[0013] An embodiment of the present invention is described below on the basis of the drawings.
Figure 1 is an explanatory diagram schematically depicting an outline of a system
configuration of an internal combustion engine 1 to which the present invention is
applied.
[0014] The internal combustion engine 1 is, for example, a multi-cylinder spark ignition
gasoline engine, and is mounted in an automobile or another vehicle. The internal
combustion engine 1 transmits, for example, rotation of a crankshaft 2 as drive force
to driving wheels of the vehicle. The internal combustion engine 1 may be a diesel
engine.
[0015] Intake air is distributed to each cylinder of the internal combustion engine 1 via
a collector 4 forming a part of an intake passage 3. An electric throttle valve 5
that adjusts the amount of air taken into the internal combustion engine 1 is disposed
upstream of the collector 4. The throttle valve 5 is equivalent to an air amount adjustment
part capable of adjusting the amount of air supplied into the cylinders, is provided
in the intake passage 3, and is positioned upstream of the collector 4.
[0016] The internal combustion engine 1 has a fuel injection valve (not shown) and a spark
plug (not shown). An amount of fuel injected through the fuel injection valve, a fuel
injection timing of the fuel injection valve, an ignition timing of the spark plug,
a pressure of fuel supplied to the fuel injection valve, and the like are optimally
controlled by a control unit 21, which will be described later.
[0017] The internal combustion engine 1 drives: an alternator 6, which generates power in
order to charge an onboard battery; a compressor 7 for an air conditioner; and the
like.
[0018] In this embodiment, the alternator 6 is a "motor generator," and is capable of driving
the crankshaft 2 of the internal combustion engine 1 by power running. In other words,
the alternator 6 is equivalent to an electric motor capable of causing the crankshaft
2 to rotate and starting (cranking) the internal combustion engine 1.
[0019] When there is a demand to drive the alternator 6, the air conditioner, and other
auxiliary devices and these auxiliary devices are driven, an auxiliary device load
is exerted on the internal combustion engine 1 and the load of the internal combustion
engine 1 increases.
[0020] Rotation of the crankshaft 2, which is transmitted via a belt 8 and a crank pulley
9, serves as a motive power source for the air conditioner and other auxiliary devices
driven by the internal combustion engine 1. The crank pulley 9 is integrally attached
to an end part of the crankshaft 2. The belt 8 is wound around the crank pulley 9
and an auxiliary-device-side pulley 10.
[0021] An electromagnetic clutch 11 for the air conditioner is provided between the internal
combustion engine 1 and the compressor 7 of the air conditioner. Specifically, the
electromagnetic clutch 11 for the air conditioner is provided between the compressor
7 of the air conditioner and the auxiliary-device-side pulley 10 to which the rotation
of the crankshaft 2 is transmitted.
[0022] The internal combustion engine 1 is disconnected from the compressor 7 of the air
conditioner by releasing the electromagnetic clutch 11 for the air conditioner. The
electromagnetic clutch 11 for the air conditioner is disengaged by a command from
the control unit 21 when the air conditioner is not used. In other words, when the
internal combustion engine 1 does not use the air conditioner, the electromagnetic
clutch 11 for the air conditioner is disengaged, and the load on the compressor 7
of the air conditioner is reduced.
[0023] Regarding those devices among the various auxiliary devices driven by the internal
combustion engine 1 that are capable of reducing the load of the internal combustion
engine 1 when disconnected from the internal combustion engine 1 when stopped, as
is the air conditioner, an electromagnetic clutch may be provided between the internal
combustion engine 1 and any of these devices, and the electromagnetic clutch may be
disengaged when the device stops.
[0024] The control unit 21 receives detection signals from a crank angle sensor 22 that
detects a crank angle of the crankshaft 2, an accelerator position sensor 23 that
detects an amount by which an accelerator pedal (not shown) is depressed, a vehicle
speed sensor 24 that detects speed of the vehicle, a brake sensor 25 that detects
an amount by which a brake pedal (not shown) is depressed, a catalyst temperature
sensor 26 that detects a catalyst temperature of an exhaust purification catalyst
(not shown) provided in an exhaust passage (not shown) of the internal combustion
engine 1, a pressure sensor 27 that detects a pressure (air pressure) in the collector
4, and other various sensors.
[0025] The control unit 21 calculates load (engine load) required by the internal combustion
engine 1 using the detection value of the accelerator position sensor 23.
[0026] The control unit 21 is capable of detecting a state of charge (SOC), which is a ratio
of a remaining charge to a charge capacity of an onboard battery (not shown). In other
words, the control unit 21 is equivalent to a battery SOC detection part.
[0027] The crank angle sensor 22 is capable of detecting an engine speed (number of engine
rotations) of the internal combustion engine 1.
[0028] When predetermined automatic stop conditions are met while the vehicle is traveling
or stopped, the fuel supply is stopped and the internal combustion engine 1 stops
automatically. The internal combustion engine 1 then restarts when a predetermined
automatic restart condition is met during the automatic stop. In other words, the
control unit 21 automatically stops the internal combustion engine 1 when the predetermined
automatic stop conditions are met, and automatically restarts the internal combustion
engine 1 when a predetermined automatic restart condition is met.
[0029] The automatic stop conditions of the internal combustion engine 1 are, for example,
that the accelerator pedal is not depressed, that the battery SOC of the onboard battery
is greater than a predetermined battery threshold SOCth, that the catalyst temperature
of the exhaust purification catalyst is higher than a predetermined first catalyst
temperature threshold T1, and the like.
[0030] The internal combustion engine 1 automatically stops when these automatic stop conditions
have all been met. In other words, the control unit 21 automatically stops the internal
combustion engine 1 when these automatic stop conditions have all been met while the
internal combustion engine 1 is operating. That is, the control unit 21 is equivalent
to a first control part that stops fuel injection to automatically stop the internal
combustion engine 1 when predetermined automatic stop conditions are met.
[0031] Conditions for automatically restarting the internal combustion engine 1 are, for
example, that the accelerator pedal is depressed, that the battery SOC of the onboard
battery is equal to or less than the predetermined battery threshold SOCth, that the
catalyst temperature of the exhaust purification catalyst is equal to or less than
the predetermined first catalyst temperature threshold T1, and the like.
[0032] The internal combustion engine 1 restarts when there is a restart request during
an automatic stop. In other words, the control unit 21 restarts the internal combustion
engine 1 when any of these automatic restart conditions is met during an automatic
stop of the internal combustion engine 1. For example, the automatically stopped internal
combustion engine 1 restarts when the battery SOC of the onboard battery becomes equal
to or less than battery threshold SOCth, which is a predetermined value.
[0033] Examples of an automatic stop of the internal combustion engine 1 include an idle
stop, a "coast stop," and a "sailing stop."
[0034] An idle stop is carried out when automatic stop conditions such as, for example,
those described above are met while the vehicle has temporarily stopped. The idle
stop is canceled when any automatic restart condition such as, for example, those
described above is met.
[0035] A coast stop is carried out when automatic stop conditions such as, for example,
those described above are met while the vehicle is traveling. The coast stop is canceled
when any automatic restart condition such as, for example, those described above is
met. A coast stop is an automatic stopping of the internal combustion engine 1 during
deceleration with the brake pedal depressed at, for example, a low vehicle speed.
[0036] A sailing stop is carried out when automatic stop conditions such as, for example,
those described above are met while the vehicle is traveling. The sailing stop is
canceled when any automatic restart condition such as, for example, those described
above is met. A sailing stop is an automatic stopping of the internal combustion engine
1 during inertia traveling with the brake pedal not depressed at, for example, a medium
to high vehicle speed.
[0037] When there has been a request to restart the internal combustion engine 1 during
a decrease in the engine speed of the internal combustion engine 1 due to an automatic
stop, the control unit 21 starts (causes combustion to occur in) the internal combustion
engine 1 by resuming fuel injection if the engine speed of the internal combustion
engine 1 is equal to or greater than a predetermined combustion recoverable rotational
speed threshold R1 (rotational speed threshold) at which restarting is possible only
by fuel injection, and rotatably drives the crankshaft 2 using the alternator 6 to
start (crank) the internal combustion engine 1 if the engine speed of the internal
combustion engine 1 is lower than the combustion recoverable rotational speed threshold
R1. Furthermore, when the engine speed of the internal combustion engine 1 falls below
the combustion recoverable rotational speed threshold R1 during a decrease in the
engine speed due to an automatic stop, the control unit 21 controls the throttle valve
5 so that the amount of air entering the cylinders is less than before the engine
speed falls below the combustion recoverable rotational speed threshold R1. That is,
the control unit 21 is equivalent to a second control part. The combustion recoverable
rotational speed threshold R1 is a value of, for example, about 600 rpm.
[0038] It is thereby possible with the internal combustion engine 1 to ensure the amount
of air in the cylinders and prepare for starting (combustion in) the internal combustion
engine 1 by resuming fuel injection when, after the automatic stop conditions have
been met, the engine speed is equal to or greater than the combustion recoverable
rotational speed threshold R1.
[0039] When the engine speed is lower than the combustion recoverable rotational speed threshold
R1 after the automatic stop conditions of the internal combustion engine 1 have been
met, it is possible to reduce compression reaction force and minimize fluctuation
in the rotation of the internal combustion engine 1 by reducing the amount of air
entering the cylinders (intake air amount). It is possible to minimize vibration in
the internal combustion engine 1 when the engine speed passes through a predetermined
resonance band (resonance range) of the internal combustion engine 1 due to the reduction
in compression reaction force caused by a reduction in the amount of air entering
the cylinders.
[0040] This resonance band corresponds to a rotational speed range (e.g., an engine speed
of 300-500 rpm) lower than the engine speed during idling of the internal combustion
engine 1. That is, the motive power transmission system of the internal combustion
engine 1 has a resonance band in which resonance occurs when the engine speed is in
a range between an engine resonance rotational speed upper limit Ru and an engine
resonance rotational speed lower limit R
L.
[0041] When the control unit 21 automatically stops the internal combustion engine 1 while
the alternator 6 is generating power or while the air conditioner is in use, the control
unit 21 stops the generating of power by the alternator 6 or the use of the air conditioner
and controls the throttle valve 5 so that the amount of air entering the cylinders
is less than before the generating of power by the alternator 6 or the use of the
air conditioner was stopped. Specifically, when the control unit 21 automatically
stops the internal combustion engine 1 during operation of the auxiliary devices driven
by the rotation of the crankshaft 2 of the internal combustion engine 1, the control
unit 21 stops these auxiliary devices and controls the throttle valve 5 so that the
amount of air entering the cylinders is less than before the auxiliary devices were
stopped.
[0042] When the throttle valve 5 is closed to reduce the amount of air entering the cylinders
(intake air amount), there is a possibility that the amount of air entering the cylinders
cannot be sufficiently reduced before the engine speed passes through the resonance
band of the internal combustion engine 1, depending on the responsiveness of the amount
of air entering the cylinders or the deceleration of the engine speed.
[0043] Therefore, when the internal combustion engine 1 is automatically stopped, the amount
of air entering the cylinders can be reduced more quickly than before the engine speed
passes through the predetermined resonance band of the internal combustion engine
1, by stopping the alternator 6, the air conditioner, and the other auxiliary devices
to reduce the amount of air needed to start combustion.
[0044] After the engine speed has passed through the predetermined resonance band of the
internal combustion engine 1, the control unit 21 increases the amount of air entering
the cylinders to be greater than when the engine speed passes through the predetermined
resonance band of the internal combustion engine 1. Specifically, when the engine
speed becomes equal to or less than the engine resonance rotational speed lower limit
R
L, the control unit 21 increases the amount of air entering the cylinders to be greater
than when the engine speed is between the engine resonance rotational speed upper
limit Ru and the engine resonance rotational speed lower limit R
L.
[0045] After the engine speed has passed through the resonance band of the internal combustion
engine 1, the influence of vibration due to the compression reaction force becomes
small. Therefore, after the engine speed has passed through the resonance band of
the internal combustion engine 1, the internal combustion engine 1 can be quickly
started when a request to restart the internal combustion engine 1 is generated, by
opening the throttle valve 5 to return the amount of air entering the cylinders to
the amount of air needed to start the internal combustion engine 1.
[0046] Figure 2 is a timing chart indicating states of control of the internal combustion
engine 1 after the automatic stop conditions have been met.
[0047] In Fig. 2, the automatic stop conditions are met at time t1. Automatic stoppage of
the internal combustion engine 1 is allowed at time t1. When automatic stoppage of
the internal combustion engine 1 is allowed, fuel injection from the fuel injection
valve is stopped in the internal combustion engine 1.
[0048] In Fig. 2, the engine speed gradually decreases from time t1 onward, and passes through
the resonance band of the internal combustion engine 1 to reach "0" at time t6. The
engine speed reaches the combustion recoverable rotational speed threshold R1 at time
t2. The engine speed enters the resonance band of the internal combustion engine 1
at time t3, and exits the resonance band of the internal combustion engine 1 at time
t4.
[0049] In Fig. 2, the electromagnetic clutch 11 for the air conditioner (A/C clutch) is
disengaged at time t1, at which the automatic stop conditions are met.
[0050] The alternator (ALT) 6 stops generating power (power is not generated) from time
t1 onward, at which the automatic stop conditions are met in Fig. 2.
[0051] When the automatic stop conditions are met, the throttle valve 5 closes in accordance
with the amount of reduction in the auxiliary device load due to the stoppage of power
generation in the alternator 6 and the stoppage of the air conditioner. That is, at
time t1, the throttle valve 5 approaches a closed throttle opening degree by an amount
corresponding to the reduction in the load (auxiliary device load) imposed on the
internal combustion engine 1 by the auxiliary devices, which are stopped when the
automatic stop conditions are met.
[0052] From time t2 onward, at which the engine speed falls below the combustion recoverable
rotational speed threshold R1, the throttle valve 5 is controlled so as to be fully
closed until time t4, at which the engine speed exits the resonance band of the internal
combustion engine 1. That is, when the engine speed of the internal combustion engine
1 falls below the combustion recoverable rotational speed threshold R1 while the engine
speed is decreasing as the automatic stop conditions are met, the throttle valve 5
is controlled so that the amount of air entering the cylinders is less than before
the engine speed fell below the combustion recoverable rotational speed threshold
R1.
[0053] At time t4, the throttle valve 5 is controlled so as to reach a predetermined first
throttle opening degree O1, which is a predetermined large opening degree. The first
throttle opening degree O1 is a larger opening degree than a starting throttle opening
degree Os, which is set when the internal combustion engine 1 is started.
[0054] That is, after the engine speed of the internal combustion engine 1 passes through
the resonance band, the throttle valve 5 is controlled so that the amount of air entering
the cylinders is greater than when the engine speed of the internal combustion engine
1 passes through the resonance band.
[0055] At time t5, the throttle valve 5 is controlled so as to reach the starting throttle
opening degree Os when an air pressure in the collector 4 reaches atmospheric pressure.
[0056] Figure 3 is a flowchart of a flow of a control for the internal combustion engine
1 in the embodiment described above.
[0057] In step S1, a determination is made as to whether or not the automatic stop conditions
of the internal combustion engine 1 have been met and an automatic stoppage of the
internal combustion engine 1 has been started. When an automatic stoppage of the internal
combustion engine 1 has been started in step S1, the routine advances to step S2.
When an automatic stoppage of the internal combustion engine 1 has not been started
in step S1, the current routine is ended.
[0058] In step S2, the alternator 6, the air conditioner, and the other auxiliary devices
are stopped, and the auxiliary device load is cut (reduced).
[0059] In step S3, the throttle valve 5 is closed according to the amount of reduction in
the auxiliary device load. The amount by which the throttle valve 5 closes increases
as the amount of reduction in the auxiliary device load increases.
[0060] In step S4, a determination is made as to whether or not the engine speed is lower
than the combustion recoverable rotational speed threshold R1. When the engine speed
is lower than the combustion recoverable rotational speed threshold R1 in step S4,
the routine advances to step S5.
[0061] In step S5, the throttle valve 5 is fully closed.
[0062] In step S6, a determination is made as to whether or not the engine speed is equal
to or less than the engine resonance rotational speed lower limit R
L. When the engine speed is equal to or less than the engine resonance rotational speed
lower limit R
L in step S6, the routine advances to step S7.
[0063] In step S7, the throttle valve 5 is brought to the first throttle opening degree
O1, which is a predetermined large opening degree, so that the pressure (air pressure)
in the collector 4 reaches atmospheric pressure in preparation for a restart.
[0064] In step S8, a determination is made as to whether or not the pressure (air pressure)
in the collector 4 has reached atmospheric pressure. When the pressure (air pressure)
in the collector 4 is at atmospheric pressure in step S8, the routine advances to
step S9.
[0065] In step S9, the throttle valve 5 is brought to the starting throttle opening degree
Os.
[0066] An embodiment of the present invention was described above, but the present invention
is not limited to the embodiment described above; various changes can be made inasmuch
as such changes do not deviate from the main point of the invention.
[0067] In the embodiment described above, the opening degree of the throttle valve 5 is
controlled to reduce the amount of air entering the cylinders when the internal combustion
engine 1 is automatically stopped, but if the internal combustion engine 1 is provided
with a variable valve mechanism capable of changing a valve timing of an air intake
valve, the amount of air entering the cylinders may be reduced using this variable
valve mechanism. Specifically, a variable valve mechanism may be used as an air amount
adjustment part that adjusts the amount of air supplied to the cylinders.
[0068] When the internal combustion engine 1 is started in normal circumstances by a driver
operating an ignition key, the internal combustion engine 1 may be started using the
alternator 6, but the internal combustion engine 1 may also be started by a dedicated
starter motor different from the alternator 6.
[0069] That is, the internal combustion engine 1 may be provided with a dedicated starter
motor different from the alternator 6.
[0070] The embodiment described above relates to a method and device for controlling an
internal combustion engine.